hydrogen production from water using solar cells powered nafion ...

total efficiencies of the fermentation systems are very low at about 5-10%. Levin and
coworkers calculated that 758m 3 of photo-fermentation bacteria tank were required to
supply a necessary amount of H 2 to a 5kW PEM fuel cell. The volume could be decreased
to 1.25m 3 for CO-oxidation bacteria bioreactor, and 1 m 3 for dark fermentation mesophilic
bacteria (Levin et al. 2004). It is projected for photo-fermentation bacteria that their low
investment costs could overcome this low efficiency problem. The major challenges for
dark fermentation and CO-oxidation bacteria are the mass transfer problems of their bio-
reactors. The researchers were not able to scale up the experiments because they cannot
achieve high reactant gas concentrations for the bacteria in the solution. High volume
hydrogen bioreactors require new reactor designs and may require radically new
technologies.
Another way to produce hydrogen is to use water electrolysis which is electricity
depended hydrogen production method. In general, electrolysis is a process that the ionic
compound is dissolved in a solvent so that its ions are available in the liquid. Current is
applied between a pair of inert electrodes immersed in the liquid. Each electrode attracts
ions which are of the opposite charge. In the water electrolysis case, cations are hydrogen
ions and anions are the oxygen atoms. The energy required to separate these ions, and cause
them to migrate to the respective electrodes, is provided by an electrical power supply.
Therefore electrolysis is an electricity depended process and it could be viable if the
electricity is cheap.
Hydrogen production using electrolysis cannot be classified as a renewable method
because it depends on the source of the electricity. For example, wind, solar PV, wave and
geothermal energies can all be a source to produce renewable hydrogen using electrolysis
while fossil or nuclear fuel based electricity depended electrolysis cannot be classified as
renewable hydrogen production. The Figure 2.1 below categorizes the hydrogen production
methods according to their energy source.
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